A prior art search disclosed the following references:
U.S. Pat. No. 3,500,251 utilizes a series of slots cut into a waveguide wall to transfer energy from one portion of an RF switch to another, wherein the slots have a gradually decreasing length as the waveguide is traversed. However, this patent teaches away from the present invention in that the waveguide tapers in the same direction that the length of the slots taper (the presence of wedge shaped dielectric 20 increases the electrical width of the waveguide), whereas in the present invention the waveguide and slots taper in opposite directions. Furthermore, the patent discloses log periodic radiators, which means that at least one slot is resonant at any particular frequency within the band of operation of the device, wherein the present invention uses slots which are solely nonresonant.
U.S. Pat. Nos. 3,530,478 and 3,633,207 show slotted waveguide antennas having slots which gradually diminish in length as one traverses the waveguide. However, in these patents the waveguide tapers in the same direction as the tapering of the slots, and furthermore, the antennas are log periodic.
U.S. Pat. No. 3,218,644 utilizes a log periodic series of slots with energy traveling between two ground planes (therefore, it is not a waveguide).
U.S. Pat. Nos. 3,987,454 and 3,990,079 are slotted waveguide antennas wherein the slots follow a log periodic function, unlike the nonresonant slots of the present invention. Furthermore, the slots are aligned with their long axes substantially parallel to the direction of propagation, rather than orthogonal thereto as in the present invention.
Hyneman, "Closely-Spaced Transverse Slots in Rectangular Waveguide", IRE Transactions on Antennas and Propagation, October, 1959, p. 335 et. seq., shows a closely spaced slotted traveling wave array. All slots have the same length, the waveguide does not taper, and the waveguide is filled with air.
Dion, "Nonresonant Slotted Arrays", IRE Transactions on Antennas and Propagation, October, 1958, p. 360 et seq, describes relationships among parameters within nonresonant slotted arrays.